The present invention relates to an accumulator fuel injection apparatus and, more particularly, to a fuel injection apparatus for a diesel engine, which facilitates setting of an amount of pre-lift of a nozzle needle.
As a fuel injection apparatus for a diesel engine, an arrangement has been disclosed, for example, in U.S. Pat. No. 5,156,132, which comprises common accumulator piping called a common rail for accumulating high-pressure fuel, and an injector for injecting the fuel. A nozzle needle for opening and closing an injection bore is slidably arranged within the injector. The nozzle needle defines a back-pressure chamber for retaining fuel pressure which acts on the nozzle needle. Pressure within the back-pressure chamber is so controlled as to be switched to fuel pressure on the high-pressure side and fuel pressure on the low-pressure side by a three-way electromagnetic valve. Thus, the high-pressure fuel supplied from the accumulator piping is injected from the injection bore. In order to improve engine performance, pre-lift of a nozzle needle is so set as to achieve boot-type injection which is such an injection rate that an amount of injection at the initial time of injection is constant, the amount of injection is made substantially constant after the amount of injection rises again, and running-out of the injection is completed instantaneously.
For the conventional fuel injection apparatus for the diesel engine having an arrangement of the kind referred to above, however, the amount of pre-lift of the nozzle needle which determines or decides the initial amount of injection is decided by the uppermost portions of the group of parts which are moved together with the nozzle needle. Accordingly, there is a problem that dimensional management or administration of a plurality of parts in a longitudinal direction and an estimate of longitudinal deformation of the parts due to hydraulic pressure are extremely difficult.